(1) Field of the Invention
The present invention relates to a process for the preparation of alkenylsuccinic anhydrides. More particularly, it relates to a process for the preparation of alkenylsuccinic anhydrides, in which formation of decomposition products of maleic acid or by-products having a high molecular weight by polycondensation is controlled and an alkenylsuccinic anhydride having a high quality can be prepared at a low temperature in a high yield.
(2) Description of the Related Art
Alkenylsuccinic anhydrides have been used as neutral sizing agents for paper, additives for lubricating oils and fuel oils for internal combustion engines, dispersants for lacquers, plasticizers, and intermediates for various chemical products. Recently, these anhydrides have become widely used as curing agents for epoxy resins, modifiers for alkyd resins, modifiers for phenolic resins, plasticizers for natural rubbers, synthetic rubbers, and thermoplastic resins such as polyvinyl chloride, dispersants, rust-preventing agents, grease, and spreaders for printing inks.
An alkenylsuccinic anhydride can be easily prepared by subjecting an olefin and maleic anhydride to an ene-addition reaction at a high temperature of 180.degree. C. to 250.degree. C. However, since the thermal reaction is carried out at a high temperature, discoloration of the product is extreme, and in many cases, by-products having a high molecular weight, sludges, tars and other undesirable by-products are formed by decomposition and polycondensation of the starting material and these by-products are incorporated in the product, resulting in an increase of the viscosity or gelation. Therefore, it is ordinarily necessary to subject the reaction product to distillation. Moreover, it is necessary to remove sludges or tars adhering to or left in the reaction vessel by washing or other means.
Various improvements for solving these problems have been proposed. For example, there can be mentioned processes disclosed in Japanese Examined Patent Publications No. 50-33,720, No. 53-2,678, No. 53-1,799, No. 52,-23,668, No. 52-39,674, and No. 52-48,639 and Japanese Unexamined Patent Publications No. 57-35,580 and No. 57-3,558. However, from the results of experiments made by us, it has been found that all of the foregoing defects cannot be completely eliminated by these improved processes.